Micro-optical electromechanical system (MEOMS) membranes are used in a spectrum of optical applications. For example, they can be coated to be reflective and then paired with a stationary mirror to form a tunable Fabry-Perot (FP) cavity/filter. They can also be used as stand-alone reflective components to define the end of a laser cavity, for example.
The MEOMS membranes are typically produced by depositing a membrane structure over a sacrificial layer, which has been deposited on a support structure. This sacrificial layer is subsequently etched away or otherwise removed to produce a suspended membrane structure in a release process. Often the membrane layer is a silicon compound and the sacrificial layer can be polyimide, for example.
Typically, membrane deflection is achieved by applying a voltage between the membrane and a fixed electrode on the support structure. Electrostatic attraction moves the membrane in the direction of the fixed electrode as a function of the applied voltage. This results in changes in the reflector separation of the FP filter or cavity length in the case of a laser.
One chronic problem associated with micro electromechanical system (MEMS) membranes in general is stiction. Specifically, if deflected sufficiently to contact an adjoining surface, the membranes can adhere to that surface because of atomic-level forces. This problem can be more intractable in the context of the optical membranes of MOEMS devices since anti-stiction coatings may be incompatible with the required optical coatings, such as antireflective (AR) coatings or dielectric highly reflecting (HR) coatings, for example. Moreover, these membranes are typically smooth because of the focus on optical performance, which smoothness typically increases the level of stiction forces in the event of contact.
In general, according to one aspect, the invention features an electrostatically driven optical membrane. It comprises a support structure and a membrane structure, which separated from the support structure by an electrostatic cavity. Stiction plugs are formed in the membrane structure. The plugs extend from a surface of the membrane. In one implementation, the plugs are hollow to allow a subsequent release process in which the sacrificial layer is removed.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.